In recent years, grid-connected wind turbine generators have been required to contribute to recovery from a change in the frequency of the utility grid (primary frequency response, hereinafter, referred to as “PFR”) within a predetermined time range (for example, within 30 seconds) from the occurrence of a disturbance in the utility grid.
U.S. Pat. No. 7,345,373 describes that, in PFR, a limit is provided for active electrical power to be output, based on the rotational speed of the rotor or generated output power.